This invention relates to programmable logic device integrated circuits, and more particularly, power supply noise monitoring in programmable logic devices.
Programmable logic devices are a type of integrated circuit that can be programmed by a user to implement a desired custom logic function. In a typical scenario, a logic designer uses computer-aided design tools to design a custom logic circuit. These tools use information on the hardware capabilities of a given programmable logic device to help the designer implement the custom logic circuit using the resources available on that device. When the design process is complete, the tools generate configuration data files. The configuration data is loaded into programmable logic devices to configure them to perform the desired custom logic function.
Logic designers must take power supply noise effects into account when designing circuitry for programmable logic devices. Particularly at high switching speeds, noise effects such as simultaneous switching noise (SSN) can adversely affect circuit performance. Simultaneous switching noise (SSN) affects circuits when a number of signals switch simultaneously. When a significant number of signals switch simultaneously, the value of the ground voltage can rise and the value of the positive power supply voltage can drop. These SSN effects, which are referred to as ground bounce and Vcc sag, may be significant enough that the digital data passing through the circuit becomes corrupted.
It is generally not possible to probe the power supply voltages on internal nodes in a programmable logic device integrated circuit. As a result, noise characterization measurements are typically made by routing internal power supply signals to external pins. By measuring the noise on these pins, a logic designer can determine how much noise margin exists in a given circuit design.
The noise characterization information that is gathered in this way can be used in optimizing the design. However, noise measurements made by routing internal signals through the device's package and the circuit board on which the device is mounted can be strongly influenced by the package and circuit board environment. Conventional power supply noise measurement arrangements are therefore often inaccurate.
It would therefore be desirable to provide programmable logic device integrated circuits with internal power supply noise monitoring capabilities.